1. Field of the Invention
The present invention generally relates both to a cooling apparatus and to a printer. In particular, it relates to a cooling apparatus for cooling a hammer coil which drives a print hammer used in a character-printing mechanism of a line printer.
2. Background Art
FIG. 1 shows one example of a conventional print hammer mechanism which is used in a character-printing mechanism of a line printer. A plurality of print hammers 51 are aligned linearly in a character printing position, and each of the print hammers 51 is normally held in a stationary position by a return spring 52 and a plunger 53. When a character is to be printed, the print hammer 51 is driven by the electrical actuation of a hammer coil 57, so that a head 58 of the hammer 51 hits a character formed on a type belt 54. Located between the head 58 and the type belt 54 are a paper sheet 55 and an ink ribbon 56 so that the character is printed on the paper 55.
In FIG. 1, a plurality of heads 58 are aligned in a direction perpendicular to the drawing, and their print hammers 51 alternate above and below the row of heads 58 with the hammer coils 57 also alternating. The distance or pitch between the neighboring heads 58 is about 0.1 inches (2.5 mm), so that the distance between the neighboring hammer coils 57 is about 0.2 inches. The latter distance or pitch is extremely small. That is, hammer coils are located extremely close to one another. Therefore, if the print hammers 51 are operated at high speed, the hammer coils 57 generate a large quantity of heat. This heat changes the electrical resistance of the hammer coil 57 and thus degrades the character printing quality. In order to eliminate this problem, cooling fins 61, as shown in FIG. 2, are disposed at the rear portion of the hammer coils 57 with their openings facing upwardly or downwardly. However, sufficient heat radiation from ambient air cooling may not be obtainable if the line printer is operated in a high speed print mode for long periods of time. Therefore, mere provision of the fins cannot solve the problems of the prior art.
In order to further improve the prior art device, as shown in FIG. 3, a proposal has been made in which a blower 71 is provided to feed cooling air, and the air is divided in a hammer duct 73 to permit the cooling air to impinge on the two sets of cooling fins 61, to thereby perform forcible cooling of the hammer coils. However, with this structure, the cooling air passing between the fins is subjected to relatively large flow resistance at a grooved portion defined by the fins since the fins 61 have a small dimension. As a result, cooling air may not pass through the entire length of the fins but may escape upwardly therefrom as shown by the arrows. Accordingly, it would be difficult to provide uniform cooling effect and to enhance cooling efficiency.